Unknown Factors
by ManOfChocolate
Summary: With the barrier destroyed, the Underground prepares to move to the Surface, at long last. Alphys invites Frisk to a little science project, during which she asks the one question that puzzles her the most: why did they climb Mt. Ebott?
**A/N: Fresh crosspost from AO3!**

 **After a little time off, this is yet another request done for a kindly Anon from the /utg/ thread. The prompt this time around was "Alphys asks Frisk why they climbed Mt. Ebott". Additional author's notes can be found at the end, to avoid spoilers. Have fun!**

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The lab was loud with what could only be described as an engine roaring at full force. Metallic clangs and steam eruptions merged together into a cacophonic symphony, resounding in every corner of the building. The machinery groaned under the immense pressure, the nuts, bolts, plates and copious amounts of duct tape barely holding it together. Every second it seemed like something would unscrew or tip over, promising nothing short of cataclysmic results.

Alphys stood among this pressurized chaos, reveling in her element. This was where she belonged now: a sweet, yet cold dance of experiments, tests and machinery. While her stature wasn't exactly the most nimble, she deftly adjusted every little lever and switch whenever the pressure exceeded even the most generous levels of dangerous. In moments such as this, she really did feel like every bit of the scientist she aspired to be from the start.

"I need more power!" she called over through the veil of steam.

Hearing no answer, she timed it just right and leaned over when the pipes were heaving for yet another blow of relief. She immediately caught sight of her little assistant, the oversized lab coat seizing them like a cocoon. Frisk's head barely stuck out of the folds, but they were quite obviously sweating from the rapidly growing heat.

"It's too dangerous!" they shouted, eying the slowly expanding bomb just behind Alphys.

"It'll be fine!" the lizard monster assured. Her eyes were no longer even visible from the corrupting touch of dark arcane science, or just the tons of steam obscuring her glasses. Even her stutter seemed to dissipate due to the immense concentration. "Just pull that lever and see for yourself!"

The last thing on Frisk's laundry list of objectives was getting within so much as sight distance of the machine, but Alphys had a steady track record of being correct at least three out of five times. Considering the Underground, those weren't bad chances at all. The human gulped and reached out, grabbing onto the last colorful lever and giving it a firm pull.

Every single warning signal went berserk.

The lights on the ceiling were blinking, the sirens on the walls were blaring, the little chimes on the pipes were ringing and they could almost hear even the CORE itself screaming in the distance. Frisk took a step back, only to get right within the reach of the former Royal Scientist, who pulled them over to herself and the infernal machine. The thing was glowing almost red-hot by now, and was not showing any signs of slowing down.

Frisk already started mentally apologizing to Sans for what would surely result in a messy RESET. By the looks of the volatile, angry hunk of metal, the human suspected they would be lucky if there would be a single speck of dust left of either of them in the next several minutes. Alphys, on the other hand, seemed more confident than ever, eyes most likely beaming with determination behind the currently-impenetrable glasses.

"Just a little more, a little bit more..." she hissed, fingers tapping across Frisk's shoulders as she held them close. They supported this notion and sunk into the pudgy monster as much as possible for safety.

The machine was now visibly rumbling, as if trying to tear itself from its binds and coils. A brief flash of Mettaton crossed Frisk's mind, but compared to the flamboyant performer, this was a much more immediate, much hotter and steamier threat. They quickly re-evaluated that assessment, but by then, the final seal was broken. The device braced itself for one solemn and explosive finish, under the excited eyes of Alphys and the terrified gaze of Frisk. The clangs, whirs and whistles all rose to a thunderous crescendo, echoing all across not just the lab, but all of Hotlands, before everything went silent and numb. A few moments later, the machine produced another halfhearted rumble and stream of orange liquid burst into the previously inserted jug.

The soda was ready.

"There we go!" Alphys chuckled, very satisfied with the results. The frosty strands trying to crawl up the side also suggested that not only did it work; the result was ice-cold, in defiance of all expectations. "Can you get the chairs please, Frisk?"

They nodded with not just a bit of relief and scurried right off, while she made sure to properly shut the machine down for good. They pulled the two chairs previously sent up using escalators to Alphys' work table. While she was still substantially behind schedule, packing for the surface did help with clearing much of the junk and various bits of paperwork she'd been stockpiling. The monster soon came along with the pitcher and two glasses.

"Do you always make soda like this?" Frisk asked once seated, still wiping leftover sweat from their brow.

"N-not always." she admitted. With the experiment over, her stutter began to resurface as well. "There's a quicker way, but this is always an i-impressive show. You should have seen Undyne the first time I did this."

Frisk couldn't help, but giggle. It wasn't hard to imagine the usually down-to-earth monster watching such a display of machine power with nothing, but overwhelming childish fascination. They waited patiently for Alphys to pour them a glass, secretly anxious to try it out. She poured some for herself as well and before Frisk could have seized their glass, clinked the two together for a quick little toast. While a little embarrassed they didn't think of that, the human took the glass and almost immediately downed half of it.

Alphys snorted and postponed drinking, as she noticed Frisk making multitudes of funny faces over the soda. None of them suggested poisoning, just a general unfamiliarity.

"You've never had soda before?" she guessed. "Undyne said you refused when she offered you some."

Frisk shook their head vigorously.

"The tea just seemed like a safer choice at the time." they admitted with a slightly embarrassed smile. The taste reminded them of several citrus fruits at the same time, but it seemed like there was a whole spectrum present in this mixture, making it difficult to tell what it really was. "It tickles!" they added, sticking just the tip of their tongue out.

"That's one reason they're so good!" she said, before remembering something and reaching into one of the drawers. She pulled out an pack of popato chisps, opened it up and placed it between them. "If we're g-going to have some junk, might as well go all out."

"Just don't tell Mom." Frisk couldn't help but glance around, as if just mentioning Toriel would summon her into the room. They wouldn't have been worried about this, if it hadn't happened several times already.

"It'll be our secret." the monster assured with a wink and sipped some of her soda.

Frisk scratched at the sides of her glass, her gaze shifting off a bit. "Are you... mad at her?"

"At Toriel? For firing me?" she asked back. She pondered a bit, but it didn't take long to formulate an answer. "N-no, not really. I can't really fault her, either."

Alphys sighed deeply, but didn't lose her smile. Frisk observed her, but at most she just looked a bit sad. "I've made m-many mistakes, some I'll remember forever. I liked being the Royal Scientist, but I'm happier without that responsibility on my shoulders. Maybe in a few years I'll apply again, but until then, I'm happy to just be a regular scientist. I'm happier as Alphys. B-besides I get much nicer lab assistants now, than I ever had as the Royal Scientist!" she added, with an honest, but still nervous and slightly even embarrassed laughter.

The child peeked around the room, suddenly noticing a lot of small-to-large objects missing since the last time they'd been here. From minor things like books and dossiers, to a couple of drawers and even the old bookshelves were missing by now. It seemed like barely a few things remained here, besides some of the machinery, household items and furniture.

"Mettaton has been sending his crew over to h-help with moving everything to the Surface." Alphys spoke up. "And Undyne's been helping o-out with a lot. A few more days and we should have everything packed and ready to go."

Frisk nodded, while taking another sip of the soda.

"Oh, I just can't wait!" the monster explained, giddy as a child. "All that stuff on the Surface! Technology, books, knowledge, all the anime! And then there's all the places we talking about with Undyne! Arcades, beaches, comic shops, dessert stalls, I have a whole alphabetical list of them!"

"Mhm."

The reaction had not gone unnoticed by Alphys. When the barrier was broken, news about it spread quickly and almost the entire Underground monster population headed straight for the exit, if only just to catch a glimpse of the outside. Under Asgore and Toriel's careful direction, the emigration from their age-old prison was a gradual, peaceful and very orderly motion. It wasn't hard to see why they had been a couple before; they complimented each other's abilities rather well and their decision-making improved substantially whenever they both had an interest in a particular issue. Yet through all the excitement and joy, there was one person in particular who didn't seem to share the same kind of wonder and overwhelming joy.

The very human who helped free all of them.

Whenever the surface came up during a conversation, Frisk gradually closed up about discussing it. They never let their feelings dampen the mood for any other monster, but she hadn't been the only one to notice they weren't fully keen on returning to her home world, despite traveling through the entire Underground just to do so in the first place. Even now, Frisk jolted as she put her glass down a little harder, their mind long trailed off.

"Frisk."

They picked their head up again to the name.

"Sooner or later, you'll hear this question from everyone, but since you're here, I get to go first." she said, trying to keep the conversation somewhat lively.

It probably would have been easier to convince Sans to take up jogging, but she still tried anyway, taking inspiration from Undyne's determination. Frisk swallowed, a ball of nerve crumpling up in their throat. They knew what was coming.

"How did you end up falling down in the first place?"

There was that question again. The one they always dreaded to hear, discuss, much less answer at all. Frisk lowered their head a bit, though since there were only the two of them right now, fading into the background was nigh-impossible.

"You're living with Toriel now. So whatever happens between them, you will see Asgore about a million times as well." Alphys continued. "They'll give you all the space you want, but e-eventually at least one of them will ask. Or Sans, or Papyrus. Undyne says she doesn't care, but, heh, she'll put you through the wringer for other stuff, I'm sure."

She chuckled to defuse the situation, but it died pretty quickly. The familiar nervousness gathered up in her by now, that keen feeling of stepping on someone's toes without meaning to. Except in most cases, she just imagined the offense, while this time Frisk did seem genuinely bothered. She sighed and ran a finger along her glass.

"Frisk? Look, I-I'm sorry, if I was being, um pushy." she spoke up again after a few moments of silence. "You don't owe me or anyone-"

"Are the cameras still on?" Frisk asked all of a sudden, with a distant hint of bitterness in their voice. They raised their head and while there was a bit of a smile, it had no soul in it.

Alphys felt her a bit of heat in her cheeks. Even if Frisk hadn't meant it, there was the very hint of an accusation in their voice. After all, out of everyone in the Underground, she had kept the closest eye on them the entire time. She pointed to the far end of the room behind her, towards a camera that was now merely gazing at the ground, with no hint it was recording, or even turned on.

"All of them are off now." she said, swallowing down her nerve to return the smile with perhaps just a bit more enthusiasm. "You won't be on the MTT News, um, not unless you really want to."

Frisk scoffed, though they quickly realized how rude that was and shook their head as well. Alphys was growing concerned by now.

"Frisk..." she said. "I mean it, you don't have-"

"There is a legend on the Surface." Frisk cut her off again, blushing a bit from the rude gesture. "They say those who go up Mt. Ebott will disappear. They also say that this isn't just a legend and that several people have disappeared around the mountain over the years."

The topic was clearly not a comfortable one, as evidenced by Frisk's balled-up fists and general lack of childish liveliness. While curiosity was a significant drive for Alphys, she was ready to cut them off the moment it became too much.

"H-have you ever met them? The other humans?" they asked, a soft tremble mixing into their voice.

"They all fell down far before my time. I've never met them. Um... at least, not in person." she admitted, involuntarily tapping the table several times with her fingers.

Frisk's throat felt surprisingly dry, but they still managed to smile just a little. It was very much like Alphys to phrase something so carefully and yet still be blatantly obvious.

"Disappearing isn't as hard as people think, it isn't even scary." they mused. "But falling down?"

The two gazed at each other for a full minute, before the child was ready to continue.

"Falling down was so scary." Frisk giggled, in-between two deep breaths. "So many monsters, so many places." they mused. "So many battles..."

The scientist felt their cheeks redden to their words. At least some of those battles were either her fault, or she had a hand in orchestrating the situation. There weren't enough words in the world to express, how sorry she was over that, even though she had already apologized so many times.

"When I had to fight Asgore," they continued. The child started swinging their feet under the chair, and licked their lips for what seemed like dozens of times already. "I didn't go to him right away. I started snooping around, trying to find something that would convince him there was another way. So, I went down some stairs..."

This time, every bit of color in Alphys' face vanished. If Frisk started poking around New Home, chances were they found exactly the worst thing they could have come across. Something even mature monsters hoped to avoid.

"And I found them. I found the other humans. And a seventh coffin." they raised their head again and for once, the former Royal Scientist could not find words to describe the look in their eyes; limitless oceans of sorrow, uneasiness, grief and guilt. "I guess that was supposed to be mine?"

"Oh god..." Alphys gasped, hand before her mouth. Frisk started shaking their head again though, their nerve coming to a boil as they weakly smacked their hand on their thigh.

"But by then, I've met Toriel, Papyrus, Sans, Undyne, Mettaton and you!" Frisk barely even noticed they had raised their voice. "And none of you would want to visit me in a coffin, that would be silly!"

And yet even those dark currents remained beneath the waves, mere phantoms of lingering emotions and thoughts. On top, smothering them were joy, happiness, humor and confidence.

"I wanted to see you all again." Frisk's voice was starting to return to its normal pitch. "And that's why I still went to Asgore. Because I knew, he would be just like all of you. Monsters with big hearts."

And love. Raw, unfiltered love. So much love it was unbearable to look them in the eyes with anything, but the purest intentions.

"Before I fell down, I was... different." they continued, twirling a lock of hair. The adorable dorky haircut was still the target of many soft jokes and teasing among monsters and Frisk took every single one of them with pride and stride. "And then I was Frisk, Frisk the human in the middle of the Underground, and I was in love with all of you." they grinned and blushed this time. "I know, this sounds pretty weird..."

It was amazing the gamut of emotions they ran through in just these several minutes. Alphys couldn't find the words and she doubted any of her books would have helped with this, either. She had no time to think at all, as those eyes were looking straight into hers, staring deep into her soul.

"What's in the lab now? The one under this?" they asked, the side of their mouth constantly trying to pull a smile even before an answer was given.

Alphys opened her mouth to answer, but the words never came out. Frisk was waiting patiently, but they weren't just looking for the clear answer, but a very specific one at that. She ran through several possibilities, only to find the answer didn't even require any deep thought.

"Nothing, but empty rooms and the Royal Scientist." she said. The way the child brightened up was a clear sign the answer was the one they sought.

"Now, we're going back to the surface." Frisk continued, with just a brief pause to take another sip of soda. "It's a whole new place for all of you, but not for me, just for Frisk. And I don't know if I can still be Frisk, when we leave."

"Why couldn't you be?" she asked. She saw a bit of confusion on Frisk's face, mostly because while they were so deep in thought, she pulled her chair closer to them. She gently took Frisk's hand and gazed right into their eyes, weathering the storm of beautiful emotions only a child could show so clearly.

"I'm not the Royal Scientist anymore, but a lot of monsters w-will call me that, because that's how they knew me. It'll be a while till they remember I'm just Alphys now." she mused, clasping Frisk's hand between her own "But you? To us, to all the monsters, you've never been anyone else, but Frisk. It doesn't matter who you were, before you, um, fell down. Nobody knows that person. But Frisk? Everyone knows Frisk!" she chuckled.

She wasn't even sure Frisk knew, but during his repairs, Mettaton asked her with uncharacteristic kindness to print and frame the ratings from when he fought Frisk. While she assumed this was just for vanity, in one of his softest moments to date, the robot admitted they wanted to forever preserve the memory of such a grandiose stage partner.

She finally let go of their hand again, giving the human just a bit of space.

"My advice? Take it from a person who, heh, already hid way too many things..." she said, ignoring the usual phantom pangs that came with the admission of guilt. "Be as honest as you want to, but Toriel, Asgore and everyone else will love you n-no matter what. They love you, Frisk, for the person they've grown to know. Nothing before that matters. If you want to stay who you are now, all you have to do is stay true to the Frisk you've been all this time."

Frisk blushed, deeply flustered by the monster's kind words. They mumbled something akin to a 'thank you', but by then their face had already turned into a miniature sun, radiating with the scorching heat of embarrassment. Reaching out for the glass, they quickly downed all the soda, along with a refill. When they were done drinking though, the smile they showed to Alphys was once again the genuine article; the kind and patient smile Frisk was known for.

"Feeling lighter now?" Alphys asked, pointing at their chest.

The child nodded with great enthusiasm. They glanced down, feeling not only their heartbeat, but in tune with it the beating of their determined SOUL. It lay dormant at the moment, but the human could still feel its brilliant glow illuminating and warming them from the inside. The feeling in their stomach was weird though, like they were still anxious about something.

The consumed fizzy goodness found its way to betray them and the moment they opened their mouth, a semi-loud burp left their throat without warning.

Frisk gasped and covered their mouth with both hands, heat in cheeks rising to a fever pitch. They glanced at Alphys in a panic, while the monster had a difficult time not just bursting into laughter on the spot.

"I'm so sorry!" their voice rose in pitch to almost a squeak. "I don't know why I did that, was that supposed to happen? Is something wrong?"

Alphys snorted loudly and couldn't hold her laughter back any longer. Frisk had closed their mouth off again, but the fizz was still active, as the monster could clearly see their cheeks expanding suddenly a few more times. Once she got over the first wave of gut-busting laughter, she quickly started to explain what happened and why.

With every word, Frisk calmed down a little more, thirsty not only for soda, but knowledge. Throughout all the explanation, which eventually required pen and paper, they still had one very specific thought in the back of they head, high over the rest. Something Sans had told them a while ago, when they faced each other down in the soft, shimmering light:

 _You never gained LOVE, but you gained love._

To Frisk, it made all the sense in the world.

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 **Post A/N: So there you have it. I didn't want to just make this into a sob story, so instead of clearly identifying a reason, I wanted Frisk to be a crafty child and dance around the issue. While this doesn't give a definitive answer, merely implications, I thought this different approach might make for a more interesting story.**

 **However, as always, the reader is the final judge on that. All I can request, is that you insert a chocolate bar within the next minute, to ensure my continued survival.**

 **I also have a tumblr at .com. There isn't much to see there, but feel free to contact me if you'd like to!**


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